Area Forecast Discussion
Issued by NWS St. Louis, MO

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331
FXUS63 KLSX 251950
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
250 PM CDT MON JUL 25 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 225 PM CDT Mon Jul 25 2016

The threat of additional showers and thunderstorms is the main
forecast issue tonight. The primary cold front appears to be
located across southern IL and southeast MO early this afternoon
with the majority of convection occurring along/ahead of it. There
however is a secondary wind shift and more defined dew point
gradient across northern MO and northern IL. This boundary is
forecast to sag southward tonight as weak high pressure continues
to settle into the mid-upper MS Valley. Aloft there are at least 3
impules upstream moving slowly east-southeast. While there is
nothing jumping out of the data, there appears to be at least a
threat of showers and thunderstorms generally across the southeast
half of the CWA due to these factors.

Glass

.LONG TERM...  (Tuesday through Next Monday)
Issued at 211 PM CDT Mon Jul 25 2016

Through the end of the week, upper level high pressure will
retrograde slightly and remained anchored in the western U.S. with
broad troffing aloft continuing and modulating in intensity across
the northeast quarter of the CONUS. Temperatures will generally be
near or slight below average. From Tuesday into Wednesday the entire
atmosphere across the region is dominated by weak flow, especially
in the lowest 2 km. The lack of a well-developed LLJ and the
parade of weak upper level impulses within the weak west-southwest
flow aloft makes for a challenging forecast for showers and
thunderstorms. Convergence is weak and subtle and model QPFs are
quiet varied. It appears the effect front will be well south
however there are hints of a subtle convergence area extending
ENE-WSW from the OH Valley to near or just south of St. Louis into
southwest MO, possibly the aforementioned secondary front. Thus
the southeast half of the CWA and especially southeast MO and
southwest IL appear to have the greatest pcpn threat.

Wednesday afternoon into Thursday night appears to be the period
with the most identifiable forcing and thus highest pops. The front
will first lift northward late Wed/Thurs and then an advancing
cold front and surface low will traverse the area Thurs night
into Friday.

A wavering frontal boundary will then be drapped across the area
late Friday into late Sunday as upper troffing persists across
the northeast quarter of the Nation. Changes in the upper air
regime are forecast early next week as there is progression in the
flow aloft, especially in the higher latitudes from the Pacific NW
into south-central Canada. This will allow the western U.S. upper
high/ridge to shift east and build into the central U.S. by
Monday, and the front to lift northward opening the doors to a
return of summer heat and humidity.

Glass

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 110 PM CDT Mon Jul 25 2016

Cold front continues to slowly sink south across forecast area. As
of 17z, it looks to be south of taf sites. Kept KUIN and KCOU
dry with north winds becoming light and variable by this evening.
By mid morning on Tuesday, winds to pickup from the northeast. As
for metro area, with boundary still close enough, some storms
continue to develop just east of KSTL, so added VCTS mention
through the afternoon hours. Otherwise, dry, MVFR conditions
expected through 01z Tuesday, then as lower levels dry out more,
cigs to lift to VFR and scatter out. Some patchy fog is possible
towards daybreak in metro area, so added mvfr mention between 08z
and 12z Tuesday.

Specifics for KSTL:
Cold front continues to slowly sink south across forecast area. As
of 17z, it looks to be south of taf sites. With boundary still
close enough, some storms continue to develop just east of KSTL,
so added VCTS mention through the afternoon hours. Otherwise, cigs
to be MVFR through 01z Tuesday, then as lower levels dry out
more, cigs to lift to VFR and scatter out. Some patchy fog is
possible towards daybreak, so added mvfr vsbys between 08z and
12z Tuesday. North winds becoming light and variable by this
evening. By 16z Tuesday, winds to pickup from the northeast.

Byrd

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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